Patients are often unable to make health care decisions for themselves near the end of life. Several recent court decisions have rejected the longstanding presumption that surrogates (i.e., family and friends) can make decisions for patients which accurately reflect the patients' preferences in these circumstances. Existing studies of surrogate decision making have sampled narrowly circumscribed populations and have important methodological limitations. These recent legal decisions and the paucity of empirical observations available suggest the need for a more systematic investigation of surrogate decision making. The major goal of this study is to explore the degree to which relatives or other surrogates can accurately predict the preferences of patients regarding life-sustaining treatments. The validity of this substituted judgment will be determined by asking patients in near terminal states what treatments they would accept or refuse in three medical circumstances, and testing for agreement with the legal surrogates' understanding of these patient preferences. A cross-sectional sample survey will be conducted with five groups of patients (AIDS, lung cancer, end-stage COPD, Class III-IV cardiomyopathy, and neuromuscular diseases) and their surrogates. A comparison group of patients and surrogates will be recruited from a general medicine clinic. Total sample size will be 300 patient/surrogate pairs. Trained interviewers will conduct the survey, using instruments which were reliable when pilot tested. Both positive and negative findings will be important. A high level of agreement between patients and surrogates would suggest that health care and judicial authorities can feel confident that substituted judgments are valid and demand no stricter standard for consent. If there is little agreement, this would suggest a strong need for education regarding advance directives. If demographic variables or diagnoses are found to be associated with different rates of agreement, this information may allow nurses and other health care professionals to focus future educational efforts in a more selective fashion.